An experimental test for indirect benefits in Drosophila melanogaster.

Rundle HD, Odeen A, Mooers AØ - BMC Evol. Biol. (2007)

Bottom Line:
Our results suggest that mating with successful males in this population provides an indirect benefit to females and that, at least in this environment, the benefit arises primarily through the production of more attractive male offspring.However, it is unclear whether this represents solely a traditional sexy sons benefit or whether there is an additional good genes component (with male offspring simply allocating their surplus condition to traits that enhance their mating success).Determining the effect of this indirect benefit on the evolution of female mate preferences (or resistance) will require comparable data on the direct costs of mating with various males, and an understanding of how these costs and benefits integrate across generations and vary among environments.

Background: Despite much empirical attention, tests for indirect benefits of mate choice have rarely considered the major components of sexual and nonsexual offspring fitness relevant to a population. Here we use a novel experimental design to test for the existence of any indirect benefits in a laboratory adapted population of D. melanogaster. Our experiment compared the fitness (mating success, longevity, and productivity) of individuals possessing genomes that derived two generations previously from males that were either entirely successful (studs) or wholly unsuccessful (duds) at achieving mates in three subsequent rounds of mating trials.

Results: Males from the stud treatment were 30% more successful on average at securing mates than males from the dud treatment. In contrast, we found no difference between treatments in measures of productivity or of longevity when measured in a mixed-sex environment. In the absence of females, however, males in the stud treatment outlived males in the dud treatment.

Conclusion: Our results suggest that mating with successful males in this population provides an indirect benefit to females and that, at least in this environment, the benefit arises primarily through the production of more attractive male offspring. However, it is unclear whether this represents solely a traditional sexy sons benefit or whether there is an additional good genes component (with male offspring simply allocating their surplus condition to traits that enhance their mating success). The lack of any detectable differences in female fitness between the two treatments suggests the former, although the longevity advantage of males in the stud treatment when females were absent is consistent with the latter. Determining the effect of this indirect benefit on the evolution of female mate preferences (or resistance) will require comparable data on the direct costs of mating with various males, and an understanding of how these costs and benefits integrate across generations and vary among environments.

Mentions:
In males, mortality rates were similar between stud and dud treatments when measured in a mixed sex milieu (their laboratory environment), but when measured in a single sex milieu, males from the stud treatment outperformed males from the dud treatment, having reduced rates of baseline mortality Fig 4A and senescence (Fig. 4B; Table 3). This treatment × milieu interaction was significant overall (Table 2), although it was non-significant when the two mortality parameters were each tested in isolation (ANOVAs testing treatment × milieu interaction for Gompertz parameter α: F1,28 = 1.48, p = 0.235; and β: F1,28 = 3.27, p = 0.081). As noted earlier, this treatment × milieu interaction was also present in average male life span (Fig. 2), although the effect was not significant (Table 2).

Mentions:
In males, mortality rates were similar between stud and dud treatments when measured in a mixed sex milieu (their laboratory environment), but when measured in a single sex milieu, males from the stud treatment outperformed males from the dud treatment, having reduced rates of baseline mortality Fig 4A and senescence (Fig. 4B; Table 3). This treatment × milieu interaction was significant overall (Table 2), although it was non-significant when the two mortality parameters were each tested in isolation (ANOVAs testing treatment × milieu interaction for Gompertz parameter α: F1,28 = 1.48, p = 0.235; and β: F1,28 = 3.27, p = 0.081). As noted earlier, this treatment × milieu interaction was also present in average male life span (Fig. 2), although the effect was not significant (Table 2).

Bottom Line:
Our results suggest that mating with successful males in this population provides an indirect benefit to females and that, at least in this environment, the benefit arises primarily through the production of more attractive male offspring.However, it is unclear whether this represents solely a traditional sexy sons benefit or whether there is an additional good genes component (with male offspring simply allocating their surplus condition to traits that enhance their mating success).Determining the effect of this indirect benefit on the evolution of female mate preferences (or resistance) will require comparable data on the direct costs of mating with various males, and an understanding of how these costs and benefits integrate across generations and vary among environments.

Background: Despite much empirical attention, tests for indirect benefits of mate choice have rarely considered the major components of sexual and nonsexual offspring fitness relevant to a population. Here we use a novel experimental design to test for the existence of any indirect benefits in a laboratory adapted population of D. melanogaster. Our experiment compared the fitness (mating success, longevity, and productivity) of individuals possessing genomes that derived two generations previously from males that were either entirely successful (studs) or wholly unsuccessful (duds) at achieving mates in three subsequent rounds of mating trials.

Results: Males from the stud treatment were 30% more successful on average at securing mates than males from the dud treatment. In contrast, we found no difference between treatments in measures of productivity or of longevity when measured in a mixed-sex environment. In the absence of females, however, males in the stud treatment outlived males in the dud treatment.

Conclusion: Our results suggest that mating with successful males in this population provides an indirect benefit to females and that, at least in this environment, the benefit arises primarily through the production of more attractive male offspring. However, it is unclear whether this represents solely a traditional sexy sons benefit or whether there is an additional good genes component (with male offspring simply allocating their surplus condition to traits that enhance their mating success). The lack of any detectable differences in female fitness between the two treatments suggests the former, although the longevity advantage of males in the stud treatment when females were absent is consistent with the latter. Determining the effect of this indirect benefit on the evolution of female mate preferences (or resistance) will require comparable data on the direct costs of mating with various males, and an understanding of how these costs and benefits integrate across generations and vary among environments.